Due to advances in electronics, the cost of digital clocks has fallen so low that they are commonly provided in numerous household devices or appliances such as microwave ovens, video cassette recorders, radios, and the like. These clocks, unlike most analog clocks, are operated by direct current at very low voltages. Thus, line power, which is typically relatively high voltage alternating current, must be stepped down to a lower voltage by a transformer means and changed into direct current by a suitable rectifier means within the device that includes the digital clock.
Unlike analog clocks which are driven by line power and which re-start when line power is restored after an interruption, digital clocks do not re-start after even a brief interruption of power. Instead, they are designed to go into a predetermined mode to indicate that a power interruption has occurred; typically, a digital clock will flash he time twelve o'clock a.m. continually until it is reset.
For a large household with numerous digital clocks, the continual resetting of digital clocks after power interruptions is a burdensome core, especially during the summer months when lightning storms can cause brief power interruptions several times a day. A recent study has indicated that most power outages last only about four seconds, but that is more than enough time to precipitate the chore of resetting digital clocks.
Devices have heretofore been developed that monitor line current, detect voltage drops, and activate backup power sources upon said detection to prevent any discontinuity in the power supplied to the protected device. One very well known device of this type is employed in connection with personal computers. Since RAM memory is lost when power is interrupted, external uninterruptable power supplies provide line current to the entire computer when line current is interrupted. These devices are expensive and therefore cannot be used to backup the power supply to digital clocks because of cost restraints. Moreover, these devices provide full power during the power outage.
What consumers need is a small, inexpensive black box that they can plug into any AC wall outlet and into which they can plug a VCR, radio, or other device that includes a digital clock as a auxiliary item. The black box would include means for detecting voltage drops of the type that herald a power interruption, and means for delivering only low current alternating line level voltage to the digital clock in the device. This device would simulate the power company in terms of voltage and frequency but be capable of supplying only small currents.
The prior art, however, neither teaches nor suggests how such a device could be provided economically. Just as significantly, the prior art doesn't even suggest that such a device should be provided. All prior art backup devices that are known deliver full power to the device or appliance when line current is interrupted. As a result, the batteries in such devices are necessarily expensive.